Dear Pietro,
this object is clearly a picture frame that is supposed to give the appearance of being made from a genuine tsuba.
I agree with Dale that this piece only looks like a tsuba. The poor workmanship and the lack of seppadai suggest a fake,
which was made for the western market to satisfy the hunger for Japanese antiques around the end of the 19th and the beginning of the 20th century
(as wonderful described by Geraint!).
For comparison here are some pictures of another ´picture frame tsuba´ out of my own collection, which unfortunately was made from a nice Choshu tsuba.
Sorry for the bad picture quality. I´ll do better when this one enters the for sale section
All the best,
Thomas